1. Field of the Invention
The present application generally relates to blade-control systems for aircraft rotors and specifically relates to a blade-pitch control system having an indexing swashplate.
2. Description of Related Art
Demand is increasing for rotary-wing aircraft, such as helicopters and tiltrotors, to provide more thrust, higher speeds, and carry heavier loads and/or heavier fuselages. Where performance criteria such as these are to be increased, the functional systems of the rotary-wing aircraft must be improved to provide the desired resultant performance enhancements. The rotor system is one of the many functional systems which require improvement in order to meet the demand for improved rotary-wing aircraft performance.
Rotary-wing aircraft have at least one rotor for providing lift and propulsion forces. These rotors have at least two airfoil blades connected to a central hub, and the hub is connected to a rotatable mast driven in rotation by an engine or motor. These blades may be adjustable for pitch angle, and the pitch angle is typically controlled by a swashplate assembly and linkage for connecting a rotating portion of the swashplate assembly to each blade.
One example of a prior-art system includes a swashplate movable in directions parallel to the mast axis toward and away from the rotor for collective control and which tilts about axes perpendicular to the mast axis for cyclic control. When the swashplate moves toward or away from the rotor, the pitch angle of each blade changes by the same amount, and in the same direction as each other blade. This collective control system, which is often referred to as a “rise and fall” system, provides for control of the thrust of the rotor, which is measured generally coaxial to the mast. On the other hand, tilting of the swashplate causes the pitch of each blade to change sinusoidally, or cyclically, as the rotor rotates, which causes the rotor to develop lift forces that vary across the plane of the rotor.
Although great strides have been made in the art of blade-pitch control systems, significant shortcomings remain.
While the system of the present application is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the system to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the application as defined by the appended claims.